The invention relates to a method for individual tracking of metallic hollow bodies, in particular of hot-formed steel tube.
In the context of optimizing quality assurance and the costs in the production process when finishing hot-formed types, backtracking of the finished product, i.e., when and where something was manufactured, is highly important.
Closely related thereto is the unique identification of each individual tube during passage through all required manufacturing and test steps. In particular in areas with a typical mass production, for example in a tube plant where hundreds or thousands of individual tubes are simultaneously transported, machined and tested, individual tracking is a central topic.
In the past, several methods have been used for identifying each individual piece in a process akin to tracking; however, such approach no longer meets today's requirements.
For example, in many situations the rolling or manufacturing batch is selected as the smallest identifiable unit, wherein typically the same melt or the same final dimension forms a batch.
The number of pieces in a batch is initially ether determined manually or with a counting device, and the failure of one or several pieces is recorded during passage through the individual stations
With larger batches, the batch is further subdivided into bundles, wherein each bundle receives a running number. The individual pieces are identified via the bundles which are mostly held together with wires, or via the batch, for example by inserting an identification card into one of the tubes with a bent wire.
Because the bundles are sometimes transported across several assembly halls, one cannot prevent that identification cards are lost or misplaced when the bundles are opened, or are mistakenly inserted into the wrong bundles.
Other systems operate with identification numbers which are either painted by hand or marked with a machine, with adhesively applied or stamped markings, or identifications engraved with lasers.
All these conventional processes have disadvantages, because the respective applied identification is either not always readable, for example the markings is located at the bottom side of the tube or the applied identification interferes with a test, for example because it causes erroneous indications in a US-test or the identification number is no longer readable due to an excessive transport speed of the tubes, or the measurement during the passage through all required manufacturing and test steps is not reliable.
DE 195 05 513 C2 discloses a method where a respective barcode with color markings is applied directly on each individual workpiece, in particular extending across the entire transverse tube circumference. The barcode can then be read independent of the circumferential position of the tube. The barcode is acquired with a video image so that the measurement is also independent of the transport direction.
This conventional method for individual tracking has several disadvantages. Because the tubes are handled when they pass through the individual manufacturing and test devices as well as when they are rolled on the roller table, the barcode applied with color markings can be damaged, thereby making it more difficult or even impossible to measure the identification optically.
For a reliable optical measurement of the barcode, the bar markings must not be selected to be too small depending on the surface quality and due to the roller-induced surface of the tubes, because frayed areas can be expected which the evaluation system is unable to distinguish as separate color bars. This necessitates an axial extent of the barcode of up to 500 mm, which is frequently rejected by customers for visual appearance reasons.
A generic method is disclosed in DE 10 2004 051 124 B3. In this method, the individual tube is provided with a unique identification extending about the entire tube circumference following a last hot-working step and automatically read as a video image in the feed region during the onward transport to the downstream processing and test stations independent of the transport direction. The unique identification is hereby applied as the data-matrix-code with multiple identical repetitions on the tube circumference.
The data-matrix-codes are here applied as a single track or as several tracks in a circular or helical manner in one or more revolutions of the tube.
The individual tracking of tubes marked with data-matrix-codes has been extremely successful in practice; however, it has been observed that markings in form of annual segments or markings in form of a helix applied continuously around the tube have several disadvantages.
With rolling tables that prevent rotation of the tube, the marking device must rotate completely about the tube in order to enable application of a marking around the entire circumference. This is quite complex as far as the supply of current via sliding contacts and the routing of cables or hoses of the marking device are concerned.
In a closed marking which extends around the tube in a circle, the track at the beginning and the end regions is frequently radially overwritten, preventing the code to be read.
It is an object of the invention to improve the conventional methods for individual tracking of hot-worked tubes so that even with roller tables that do not permit rotation of the tube, marking with a unique identification in form of a data-matrix-code which repeats identically multiple times on the tube circumference is possible in a simple and cost-effective manner and that the track having a circular arrangement can be reliably prevented from being overwritten.